Here in Vancouver, BC, we have to pass an emissions test. Mine failed the idle test. The hydrocarbons reading was 1354 ppm and the max allowable is 928 ppm. All other readings were fine. Anyone know what I can do or what causes high hydrocarbon readings?

I've read that it is unburned fuel. I went in with 94 octane gas and have heard that the higher the octane level the harder it is to burn the fuel. I've also heard that a new distributor and electronic ignition from MSD with their multi-spark system (I'm planning to do this anyway) will help burn the fuel.

Any suggestions??

Thanks

 

sounds like the idle mixture is a little rich. Run the idle mixture screws in untill the idle speed starts to slow and have it rechecked. Does it check any other exhaust gas when the inspection is done. If so do you know what they are?

 

That information is false. The higher the octane the more "patient" the fuel is. In other words, the fuel can wait longer for the flame front from the spark plug to get to it. It will be less likely to pre-detonate.

You are correct that hydrocarbons are unburnt fuel. I saw on tv that you can get something that goes on the exhaust and will get really hot and burn up the unburnt fuel, i think it is basically a catalytic converter. It was on that Rousch show or some other show like that, i can't remember, the one where they get cars ready for auction. They were making a classic into a more environmentally friendly car.

 

Move to Texas....if your car is over a certain age you don't have to mess with emissions testing here :-)

 

Move to Oklahoma, no emissions testing for ANY car, no matter how old or new :P

I have heard that you can pour a bottle of alcohol in your tank to help reduce HC readings

 

next time you take it in for a test drive the hell out of it on the way there. My work truck failed once and the guy doing the test told me to drive it hard and bring it in hot and it did the trick.

 

Yeah sounds like its too rich and 94 octane is too much these engines where made to run on 87 octane.

 

Snorulz, that's not how it works. The higher the octane rating for gasoline, the more stable it is, meaning it tends to be harder to ignite and burns slower compared to lower octane gas. It needs more compression to burn properly.

94 octane is too much for most engines. The only reason you'd need that much would be if you were running forced induction or very high compression. That high of an octane rating in a car that will run fine on 87 or 89 will be very difficult to ignite and will be burning in the chamber long after the ideal portion of the power stroke, leaving excess hydrocarbons in the exhaust. To compensate, you'd need to advance the timing, but even that only gets you so far.

Kurupt, you need to start at the basics. If it hasn't been done, give the car a tune up. Plugs, wires, cap, rotor, points (or electronic conversion; that MSD box may be a good idea for you), and set the timing. Also be sure to adjust the idle mixture properly, as has been mentioned.

 

yah. have to agree here. the higher the octane the harder it is to burn. if you use low octane in a car that needs high octane the fuel will end up igniting too soon/early.
Modern cars have a knock sensor (ping sensor) so you don't have to set the octane level manually anymore. they measure (or better listen for) pre-detonation.

short story: if you use 92 octane and adjust your timing to the very last stretch and then change over to 87 fuel your engine will ping

as for the unburnt fuel.
did they test that in idle? if yes you already might get away with just leaning the idle mixture screws a bit.

But it could be any fault in ignition as well. if once cylinder is not firing properly (or not at all) you'll end up with fuel in the exhaust.

There are burners for the exhaust to get rid of the excess fuel. But I'd rather fix ignition and adjust carb then burning unused fuel.

unburnt fuel==bad gas mileage

 

You are both wrong, that is a common misconception of octane numbers. I just sat through a week of lectures on that topic last semester from a guy that knows more about the auto industry and everything to do with it than majority of the people on this board combined.

The flame velocity is not affected by the octane of the fuel.

Here is something i typed up on another forum, also threw in some information on gasoline in general. I am sure this will stir the pot.

"I am currently taking an engine course the the university i attend. Over the past few lectures we have been discussing octane numbers and what they really are. I found it very interesting and wanted to share it with everyone.

First off, i will tell you what Octane numbers are NOT!
Octane numbers are not a measure of energy in one fuel!
Octane numbers are not a measure of burning velocity!
Octane numbers are not a measure of combustion temperature!

These are all common misconceptions about the mysterious number on the pump.

If you want the short and narrow, octane numbers are on the verge of worthless, to explain this i will explain how octane numbers are obtained.

I am sure you all remember seeing on the pump (R+M)/2 for the octane number. When a refinery calculates the O# (octane number) they take the Research octane number and add it to the Motor octane number and take the average. These two numbers are calculated on the same special engine but at different operating conditions. If you want an explanation of the engine and how it determines the O# just ask. The conditions for the Research number are closest to cruising down the interstate and the conditions for the Motor Octane number would be more extreme and closer to doing a WOT run.

Here lies the problem, say you have a fuel with a RON of 100 and a MON of 80. At the pump that would have a 0# of 90. If doing a WOT run your engine will be seeing the 0# of 80. Now if a fuel has a RON of 95 and a MON of 85 it will still have a pump O# of 90 but your car will see a 0# of 85 during the WOT run. As you can see, the pump O# does not really tell you much about the actual fuel. On average there is a 10 point difference between the RON and MON.

Now you may ask where the octane number comes from in the first place. Well a long time ago, someone decided that iso-octane would have a octane number of 100 and heptane would have a O# of 0. When they test a fuel, they run it in a engine with a variable compression ratio and change that ratio until it knocks with the test fuel. They then mix iso-octane and heptane until they get a ratio that makes the same level of knock at that specified compression ratio. What ever percent the mixture is of iso-octane, that is the octane number. So 87% iso-octane and 13% heptane will be 87 octane.

Octane numbers simply give you an idea of how "patient" the fuel is. This "patience" is the fuel resisting combustion until a spark is made from the spark plug. That is why a higher octane number will resist knock. So an octane number tells you what fuel will resist knock more when compared to another fuel. It is only this and nothing more. Higher octane fuels can make a difference in power but only because newer cars will retard timing when the engine knocks. As you know this will reduce your hp. Knock in itself will also reduce hp of an engine so engines without knock sensors are capable of seeing a difference in performance but the extra cost is not really worth it unless you are risking the destruction of your engine such as our case.

Now i will talk about the issue with gasoline and the fact you have no idea what you are buying. As i mentioned before, when you buy gas at the pump you don't really know what the octane level at wot conditions will be. This just gets worse when you understand how gasoline is shipped. The gasoline leaves the refinery and is pumped in a pipeline to a distribution hub where it is sent out in trucks. All the refinery's will put their fuel into the same pipeline at the same time so when the shell truck pulls up to pickup its fuel, it could be picking up amaco, bp, shell or another brand. It will most likely be getting a mix. This causes every refinery to try to meet only the basic requirements for the octane level they are sending down the pipeline. Why would Shell spend extra money on refining when for all they know, Amaco could end up with shell's fuel that they spent extra money on. The only difference in different brands of major fuel stations is in what additives they add since these are added after the pipeline.

Now it is time to change from 87 octane to 93 octane, the pipeline does not shut down, they just switch grades and now all of the refineries will pump out 93 octane. This will cause a "slug" of gas between the pure 87 and pure 93 octane to mix. This is then sold to discount gas stations since they have no idea what it really is and can't charge the same for it. Discount stations will also have cheaper additives. The flow in the pipeline is laminar to reduce mixing and because of that it takes 1 month for the fuel to get from the gulf to new york.

If you want to know exactly what fuel you are buying, you need to purchase Amaco Ultimate. They do a special extra refining process and because of that, they " buy" the pipeline for a period of time and during that time they will be the only ones pumping gasoline into it and then their trucks pick it up. This cost money so you will not find Amaco Ultimate for less but you know you are getting Amaco gasoline.

The moral of the story, is scan your car and never stop scanning because you really have no idea what you are putting in your tank.If you have an Amaco station around, you might want to consider using them."